<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn">send</button>
</body>
<script>
    const btn = document.querySelector("#btn")
    btn.onclick = ()=>{
        fetch("http://localhost:3000/api3").then(res=>res.json()).then(res=>{
            console.log(res);
        })
    }
</script>
</html>